Northward expanding resident species benefit from warming winters through increased foraging rates and predator vigilance

Abstract

Species distributions shift northwards due to climate change, but the ecological mechanisms allowing range expansions are not fully understood. Most studies have concentrated on breeding seasons, but winter warming may also be important. Wintering distributions are restricted by food availability and temperature, which may also interact. Foraging in cold conditions requires adaptations as individuals have to be efficient in foraging, while staying warm and vigilant for predators. When the ambient temperature declines, foraging rates should be reduced due to increased time spent on warming behaviours. In addition, predator vigilance should decline, because more time has to be invested in foraging. Cold weather should limit northward expanding southern species in particular, while northern species should perform better in cold conditions. We tested this by studying temperature responses (between 0 and − 35 °C) among wintering birds at feeders. We compared foraging behaviours of two northward expanding southern species, the great tit (Parus major) and the blue tit (Cyanistes caeruleus) to a northern species, the willow tit (Poecile montanus). Foraging rate and vigilance decreased, and warming behaviour increased when temperatures declined. Importantly, the performance in these traits was poorer in the southern species compared to the willow tit. Furthermore, the response to decreasing temperatures in foraging rates and warming behaviour was stronger in the great tits than willow tits. As the winters become warmer, these mechanisms should increase wintering success of southern species wintering at high latitudes, and lead to higher survival, increased population growth, and consequent range expansion.Electronic supplementary materialThe online version of this article (10.1007/s00442-018-4271-7) contains supplementary material, which is available to authorized users.

How extreme is extreme? Demographic approaches inform the occurrence and ecological relevance of extreme events

“…, Pakanen et al. ). In support of this, we found that birds were more likely to be detected at feeders during periods of more favorable (warmer, drier) weather conditions, suggesting greater use of supplemental feeding stations on mild, precipitation‐free days.…”

“…This may be especially true during extremely cold weather when the energy costs of foraging may outweigh the potential energy gains, resulting in an increased likelihood of energy shortfall (Brittingham and Temple 1988). On the other hand, if birds could fully meet their daily energy requirements, being partially determined by short-term fluctuations in minimum temperatures, they could minimize their longer-term risk of starvation by foraging more intensively when weather conditions become more favorable (Turcotte and Desrochers 2008, Vill en-P erez et al 2013, Pakanen et al 2018. In support of this, we found that birds were more likely to be detected at feeders during periods of more favorable (warmer, drier) weather conditions, suggesting greater use of supplemental feeding stations on mild, precipitation-free days.…”

Differential Long-Term Population Responses of Two Closely Related Human-Associated Sparrow Species with Respect to Urbanization

“…Climatic factors might impact the distribution and range shift of wintering bird species [36,37], especially the southerly distributed species, such as the Eurasian Tree Sparrow. For example, according to Burnett [33] the non-native Eurasian Tree Sparrow has extent of a great northward range expansion in USA, and Graham et al [73] suggested that under projected climate change scenarios, the distribution and range of the non-native Eurasian Tree Sparrow will increase markedly in the USA in the near future.…”

“…However, for example, Mohring et al [69] did not detect influences of weather conditions for the House Sparrow population changes in Paris during 2003-2017. Additionally, our data collected during 1991-2020 does not give any indication that climatic change would have influenced the growth rates of the two sparrow species, even if we conducted our study in northern latitudes where climatic factors are estimated to be important factor affecting bird populations in natural habitats [36,37]. However, the positive population growth rate of the House Sparrow was observed in some northern study sites, and population increase in the Eurasian Tree Sparrow seems to be greater in the north than in the south.…”

“…Most of the earlier sparrow studies have been performed during the breeding seasons, despite the fact that winter conditions and the recent warming of winters may have important consequences for the distribution and abundance of resident sparrow species (see, e.g., [34,35]). Sparrows' winter distribution ranges, occupancy and abundance may be restricted by several factors, such as the temperature, food availability, behavioral adaptations and urbanization, which all may also interact [36,37]. Therefore, winter season studies may give new insights into the causes of the population change of sparrows.…”